First the "turn signal devices" are nothing more than a stack of switches. With a couple of relays (or transistors) a toggle switch (double throw + neutral) or even 3 button switches could be wired to do the job. There is a wiring diagram posted here:
https://www.pinterest.com/pin/527976756306148232/.
Other options for mounting the lamp besides the bumper include inside the grille, on 1936's inside the horn grille. 1970's Chrysler turn signal indicators that mounted on top of the fenders were popular once with street rodders but are now hard to find.
You will be making a modification that will push the car gently in the direction of "street rod"... so be creative! And enjoy. There is no right or wrong, its your car.